1. Field of the Invention
This invention relates to a shutter travel completion signal producing device for a photographic camera and more particularly to an improvement of a shutter travel completion signal producing device adapted for a camera of the type having a shutter operated by a reciprocating motion of shutter blades or a shutter blade driving member for which my copending U.S. patent application Ser. No. 279,222 was filed June 30, 1981 also relates.
2. Description of the Prior Art
Generally, a photographic camera is required to have some means for giving a signal representative of completion of the opening and closing operation of a shutter to an applicable part of the camera, because: After the shutter operation, a film winding action must be allowed to take place either by effecting power supply to a winding motor if the camera is of the type having an automatic winding function or by releasing a safety arrangement for winding if the camera is of the manual winding type. In addition to this purpose, the shutter travel completion signal, or a shutter closure signal, is also used for the purpose of releasing a release button depressing operation permitting mechanism to enable a release action again to take place.
In the case of a conventional shutter device of the type arranged to open and close the shutter by rotating a shutter driving member in one direction with a charged spring, the above-stated shutter closure signal is readily obtainable with a desired acting force through a sensing lever disposed in the rotation stopping position of the shutter driving member. However, in a shutter device of another type arranged to open and close the shutter by a reciprocating motion of the shutter blades or a shutter driving member, the shutter blade or the shutter driving member takes the same phase before opening of the shutter and after closing of the shutter. In other words, the position of the shutter blade before opening of the shutter is the same as the position thereof after closing thereof. Therefore, the arrangement of the sensing lever is not applicable to such a shutter device. Accordingly, the above-stated shutter closure signal has been not simply obtainable in the case of the shutter device of that type.
Particularly, in an electromagnetic shutter device which is arranged to cause a reciprocating motion of shutter blade by an electromagnetic force, the shutter blade driving electromagnetic force is hardly obtainable in sufficiently large magnitude for having a shutter closure signal produced by the shutter blade or a shutter driving member. This problem has been hindering cameras of the type having such a shutter device from being readily practicalized.
To solve this problem, the copending U.S. patent application Ser. No. 279,222 has previously proposed a device which is characterized in that: A light sensitive element is disposed in the rear of an auxiliary stop blade arrangement which is arranged to be movable together with shutter blades and to form an aperture corresponding to the aperture of the shutter blades. The output of the light sensitive element produced when a light flux from an object to be photographed is blocked by the auxiliary stop blade at the time of shifting of the shutter blades from an open state to a closed state is used for forming a shutter closure signal.
However, this arrangement of the prior art has presented a problem that the shutter blades often bounce at the time of shifting from the open state to the closed state. In other words, the shutter blades bounce somewhat backward from a closed state in the opening direction thereof, although the shutter at that time is kept closed by the overlapping arrangement of a plurality of shutter blades. In such a case, the auxiliary stop blade also bounces together with the shutter blades. The auxiliary stop blade takes an operative phase preceding the main aperture (shutter blade aperture) in order to compensate the exposure amount at a high brightness so that it is very likely that the auxiliary stop blade unduly opens if the shutter blade bounds for some reasons, although the main aperture does not open. In such a case, the shutter closure signal which has been obtained in the manner as described above would be nullified by the bounce of the shutter blades. Conversely, it is also possible that a bounce of the shutter blades might produce a false shutter closure signal. An ordinary electric shutter of the type having shutter blades opened and closed by an electromagnet is also not free from this problem.